The microbiological assays developed in our laboratory are used to determine the distribution kinetics of methotrexate (MTX), cytosine arabinoside (ara-C), citrovorum factor (CF) and 5-methyltetrahydrofolate (5-MeTHFA). We aim to provide a quantitative means to relate toxic symptoms with the tissue and/or body fluid levels of drugs in patients. We propose to continue this study and gather sufficient data to establish such a relationship. (In collaboration with Drs. Gerald Rosen and William R. Shapiro). Several chemotherapeutic agents, besides those mentioned above are used either singly or in combination with other drugs or antibiotics. Assay methods will be developed for these agents. We propose to isolate mutants resistant to such anticancer agents or antibiotics. Isolation of antibiotic (tetracycline, gentamicin, oxacillin, ampicillin and cephalothin) resistant mutants of strains used for the assay of MTX, ara-C, CF and T-MeTHFA are in progress. The resistant strains will be examined for the physiological alterations associated with the newly acquired drug resistance. MTX is metabolized by intestinal flora. Antibiotic administration alters the physiological distribution of MTX significantly. With the use of animal models, the alteration of physiological disposition of MTX following antibiotic administration is proposed to be studied.